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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \example itemviews/fetchmore |
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44 \title Fetch More Example |
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45 |
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46 The Fetch More example shows how two add items to an item view |
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47 model on demand. |
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48 |
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49 \image fetchmore-example.png |
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50 |
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51 The user of the example can enter a directory in the \gui |
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52 Directory line edit. The contents of the directory will |
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53 be listed in the list view below. |
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54 |
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55 When you have large - or perhaps even infinite - data sets, you |
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56 will need to add items to the model in batches, and preferably only |
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57 when the items are needed by the view (i.e., when they are visible |
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58 in the view). |
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59 |
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60 In this example, we implement \c FileListModel - an item view |
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61 model containing the entries of a directory. We also have \c |
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62 Window, which sets up the GUI and feeds the model with |
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63 directories. |
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64 |
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65 Let's take a tour of \c {FileListModel}'s code. |
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66 |
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67 \section1 FileListModel Class Definition |
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68 |
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69 The \c FileListModel inherits QAbstractListModel and contains the |
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70 contents of a directory. It will add items to itself only when |
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71 requested to do so by the view. |
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72 |
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73 \snippet examples/itemviews/fetchmore/filelistmodel.h 0 |
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74 |
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75 The secret lies in the reimplementation of |
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76 \l{QAbstractItemModel::}{fetchMore()} and |
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77 \l{QAbstractItemModel::}{canFetchMore()} from QAbstractItemModel. |
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78 These functions are called by the item view when it needs more |
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79 items. |
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80 |
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81 The \c setDirPath() function sets the directory the model will |
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82 work on. We emit \c numberPopulated() each time we add a batch of |
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83 items to the model. |
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84 |
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85 We keep all directory entries in \c fileList. \c fileCount is the |
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86 number of items that have been added to the model. |
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87 |
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88 \section1 FileListModel Class Implementation |
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89 |
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90 We start by checking out the \c setDirPath(). |
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91 |
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92 \snippet examples/itemviews/fetchmore/filelistmodel.cpp 0 |
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93 |
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94 We use a QDir to get the contents of the directory. We need to |
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95 inform QAbstractItemModel that we want to remove all items - if |
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96 any - from the model. |
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97 |
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98 \snippet examples/itemviews/fetchmore/filelistmodel.cpp 1 |
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99 |
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100 The \c canFetchMore() function is called by the view when it needs |
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101 more items. We return true if there still are entries that we have |
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102 not added to the model; otherwise, we return false. |
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103 |
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104 And now, the \c fetchMore() function itself: |
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105 |
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106 \snippet examples/itemviews/fetchmore/filelistmodel.cpp 2 |
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107 |
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108 We first calculate the number of items to fetch. |
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109 \l{QAbstractItemModel::}{beginInsertRows()} and |
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110 \l{QAbstractItemModel::}{endInsertRows()} are mandatory for |
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111 QAbstractItemModel to keep up with the row insertions. Finally, we |
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112 emit \c numberPopulated(), which is picked up by \c Window. |
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113 |
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114 To complete the tour, we also look at \c rowCount() and \c data(). |
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115 |
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116 \snippet examples/itemviews/fetchmore/filelistmodel.cpp 4 |
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117 |
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118 Notice that the row count is only the items we have added so far, |
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119 i.e., not the number of entries in the directory. |
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120 |
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121 In \c data(), we return the appropriate entry from the \c |
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122 fileList. We also separate the batches with a different background |
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123 color. |
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124 */ |
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125 |